Switch control systems for light emitting diodes and methods thereof

ABSTRACT

System and method for controlling one or more light emitting diodes. For example, the system for controlling one or more light emitting diodes includes a current generator configured to generate a first current flowing through one or more light emitting diodes. The one or more light emitting diodes are configured to receive a rectified voltage generated by a rectifying bridge coupled to a TRIAC dimmer. Additionally, the system includes a bleeder configured to receive the rectified voltage, and a controller configured to receive a sensing voltage from the current generator and output a control signal to the bleeder. The sensing voltage indicates a magnitude of the first current.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/809,447, filed Mar. 4, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/124,739, filed Sep. 7, 2018, which claimspriority to Chinese Patent Application No. 201710557179.4, filed Jul.10, 2017, all of the above-referenced applications being incorporated byreference herein for all purposes.

2. BACKGROUND OF THE INVENTION

Certain embodiments of the present invention are directed to circuits.More particularly, some embodiments of the invention provide switchcontrol systems for light emitting diodes (LEDs). Merely by way ofexample, some embodiments of the invention have been applied to LEDlighting systems. But it would be recognized that the invention has amuch broader range of applicability.

As a new energy-saving and environmentally-friendly light source, lightemitting diode (LED) is widely used in various fields due to its highluminance, low power consumption and long life span. For example, withina range close to a rated current, luminance of an LED often is directlyproportional to the current flowing through the LED but is independentof the voltage across the LED; therefore LED is often supplied withpower from a constant current source during operation.

FIG. 1 is an exemplary circuit diagram showing a conventional linearconstant current LED lighting system 100 with a Triode for AlternatingCurrent (TRIAC) dimmer. The system 100 is widely used in various fieldssuch as LED lighting due to the system's simple and reliable structureand low cost. As shown in FIG. 1 , the main control unit of the system100 includes a constant current (CC) unit 110 and a bleeder unit 120.The constant current unit 110 is used for constant current control ofthe LED lighting system 100. The bleeder unit 120 is used to generate acurrent sufficient to maintain the TRIAC dimmer during normal operationand thus prevent the TRIAC dimmer from malfunctioning. A malfunction mayoccur if the current flowing through the TRIAC dimmer falls below aholding current.

As shown in FIG. 1 , after the system 100 is powered on, an AC inputvoltage (e.g., VAC) is received by a TRIAC dimmer 190 and subjected to afull-wave rectification process to generate a rectified voltage 101(e.g., VIN). For example, the rectified voltage 101 does not drop below0 volt. In one example, there is a capacitor that includes one terminalconnected to the output of the bleeder unit 120 and another terminalgrounded. In another example, there is no capacitor that includes oneterminal connected to the output of the bleeder unit 120 and anotherterminal grounded. After the system 100 is powered on, the amplifier U11inside the constant current unit 110 controls the voltage of the gateterminal of the transistor M1, so that the transistor M1 for powerregulation is closed (e.g., the transistor M1 being turned on).

After the system 100 is powered on, the error amplifier U11 of the maincontrol unit controls the voltage of the gate terminal, so that thetransistor M1 for power regulation is closed (e.g., the transistor M1being turned on). As an example, the voltage 101 (e.g., VIN) is higherthan a minimum forward operating voltage of the LED, and a current flowsthrough the LED to a sensing resistor R1 via the transistor M1, whereinthe magnitude of the voltage (e.g., V_(sense)) across the resistor R1corresponds to the current flowing through the LED. The amplifier U11receives the voltage V_(sense) at one input terminal and receives areference voltage V_(ref) at another input terminal, and performs anerror amplification process on the voltage V_(sense) and the referencevoltage V_(ref) in order to adjust the gate voltage of the powerregulation transistor M1 and realize constant current control for theLED. The output LED current I_(led) (e.g., the current flowing throughthe LED) is shown in Equation 1:

$\begin{matrix}{I_{led} = \frac{V_{ref}}{R_{1}}} & ( {{Equation}\mspace{14mu} 1} )\end{matrix}$where R₁ represents the resistance of the resistor R1, and V_(ref)represents the reference voltage.

Due to the dimming function of the TRIAC dimmer 190, the rectifiedvoltage 101 (e.g., VIN) received by the anode of the LED usually has awaveform of an AC signal that has been rectified and clipped. As anexample, when the AC signal is relatively small in magnitude within anAC cycle (e.g., when the TRIAC dimmer 190 is turned off, or during thevalley stage in magnitude for the AC signal), the LED does not conductcurrent because of the insufficient voltage and does not have a currentflowing through.

As a result, taking into account these scenarios, the output LED currentI_(led) (e.g., the current flowing through the LED) is shown in Equation2:

$\begin{matrix}{I_{led} = {\frac{V_{ref}}{R_{1}} \times \frac{T_{on}}{T}}} & ( {{Equation}\mspace{14mu} 2} )\end{matrix}$where T represents one period of the AC input voltage (e.g., VAC), andT_(on) represents time duration for conduction of the LED during oneperiod of the AC input voltage (e.g., VAC).

Therefore, the bleeder unit 120 needs to generate an output current thatis sufficient to maintain the normal operation of the TRIAC dimmer 190.From the perspective of system power, the input power of the system 100includes mainly the LED power and the bleeder power:P _(in) =P _(led) +P _(bleeder)  (Equation 3)where P_(in) represents the input power of the system 100, P_(led)represents the power consumed by the LED, and P_(bleeder) represents thepower consumed by the bleeder unit 120.

The resulting issue is that the power consumed by the bleeder unit 120affects the operation efficiency of the system 100 as shown in Equation4:

$\begin{matrix}{\eta = {\frac{P_{led}}{P_{led} + P_{bleed}} \times 100\%}} & ( {{Equation}\mspace{14mu} 4} )\end{matrix}$where η represents the operation efficiency of the system 100. Asindicated in Equation 4, if the power consumed by the bleeder unit 120is too large, the operation efficiency of the system 100 often cannot beguaranteed.

Hence it is highly desirable to improve switch control systems for LEDs.

3. BRIEF SUMMARY OF THE INVENTION

In view of one or more problems described above, certain embodiments ofthe invention provide switch control systems for LEDs.

Some embodiments of the present invention provide a high-efficiencyTRIAC dimmer switch control system for an LED lighting system and amethod of using such switch control system. For example, the TRIACdimmer switch control system reduces unnecessary power loss withoutaffecting the normal operation of the LED lighting system in order toincrease system efficiency by controlling the bleeder circuit. As anexample, the control method may be applied to a linear constant currentLED lighting system using a TRIAC dimmer.

In certain embodiments, an LED switch control system includes a constantcurrent control unit, a bleeder unit, a bleeder control unit, and arectifier unit. For example, the constant current control unit iscoupled to a transistor and configured to output a first current. As anexample, the bleeder unit is coupled to a system input and the bleedercontrol unit. For example, the bleeder control unit is coupled to theconstant current control unit and the bleeder unit and configured toreceive a sensing signal. As an example, the rectifier unit isconfigured to rectify and filter an input voltage of the system andtransmit a rectified voltage to the bleeder unit and the constantcurrent control unit. For example, the bleeder control unit isconfigured to generate a control signal to disable the bleeder unit whenthe sensing signal satisfies a first condition and to generate thecontrol signal to enable the bleeder unit to output a bleeding currentwhen the sensing signal does not satisfy the first condition. In someembodiments, an LED lighting system including an LED switch controlsystem is provided.

According to certain embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes are configured to receivea rectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator and output a control signalto the bleeder. The sensing voltage indicates a magnitude of the firstcurrent. The controller is further configured to generate the controlsignal to turn off the bleeder if the sensing voltage satisfies a firstcondition so that the bleeder does not generate a second current, andgenerate the control signal to turn on the bleeder if the sensing signalsatisfies a second condition so that the bleeder generates the secondcurrent. The second current is larger than zero in magnitude. The secondcondition is different from the first condition.

According to some embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes are configured to receivea rectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator, receive an input voltagegenerated by a voltage divider, and output a control signal to thebleeder. The sensing voltage indicates a magnitude of the first current,the voltage divider is configured to receive the rectified voltage, andthe input voltage indicates a magnitude of the rectified voltage. Thecontroller is further configured to generate the control signal to turnoff the bleeder if the sensing voltage and the input voltage satisfy afirst condition so that the bleeder does not generate a second current,and generate the control signal to turn on the bleeder if the sensingsignal and the input voltage satisfy a second condition so that thebleeder generates the second current. The second current is larger thanzero in magnitude. The second condition is different from the firstcondition.

According to some embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes is configured to receive arectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator, the sensing voltageindicating a magnitude of the first current, receive an input voltagegenerated by a voltage divider, the voltage divider being configured toreceive the rectified voltage, the input voltage indicating a magnitudeof the rectified voltage, and output a control signal to the bleeder.The controller is further configured to generate the control signal toturn off the bleeder if the input voltage satisfies a first condition sothat the bleeder does not generate a second current, and generate thecontrol signal to turn on the bleeder if the input voltage satisfies asecond condition so that the bleeder generates the second current. Thesecond current is larger than zero in magnitude. The second condition isdifferent from the first condition.

According to certain embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes are configured to receivea rectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator, receive an input voltagegenerated by a voltage divider, and output a control signal to thebleeder. The sensing voltage indicates a magnitude of the first current,the voltage divider is configured to receive a dimmer output voltagegenerated by the TRIAC dimmer and received by the rectifying bridge, andthe input voltage indicating a magnitude of the dimmer output voltage.The controller is further configured to generate the control signal toturn off the bleeder if the sensing voltage and the input voltagesatisfy a first condition so that the bleeder does not generate a secondcurrent, and generate the control signal to turn on the bleeder if thesensing signal and the input voltage satisfy a second condition so thatthe bleeder generates the second current. The second current is largerthan zero in magnitude. The second condition is different from the firstcondition.

According to some embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes are configured to receivea rectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator, receive an input voltagegenerated by a voltage divider, and output a control signal to thebleeder. The sensing voltage indicates a magnitude of the first current,the voltage divider is configured to receive a dimmer output voltagegenerated by the TRIAC dimmer and received by the rectifying bridge, andthe input voltage indicates a magnitude of the dimmer output voltage.The controller is further configured to generate the control signal toturn off the bleeder if the input voltage satisfies a first condition sothat the bleeder does not generate a second current, and generate thecontrol signal to turn on the bleeder if the input voltage satisfies asecond condition so that the bleeder generates the second current. Thesecond current is larger than zero in magnitude. The second condition isdifferent from the first condition.

According to certain embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving the rectified voltage, receiving a sensingvoltage, the sensing voltage indicating a magnitude of the firstcurrent, and outputting a control signal to a bleeder. The outputting acontrol signal to a bleeder includes generating the control signal toturn off the bleeder if the sensing voltage satisfies a first conditionso that the bleeder does not generate a second current, and generatingthe control signal to turn on the bleeder if the sensing signalsatisfies a second condition so that the bleeder generates the secondcurrent. The second current is larger than zero in magnitude. The secondcondition is different from the first condition.

According to some embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving a sensing voltage, the sensing voltageindicating a magnitude of the first current, receiving an input voltage,the input voltage indicating a magnitude of the rectified voltage, andoutputting a control signal to the bleeder. The outputting a controlsignal to the bleeder includes generating the control signal to turn offthe bleeder if the sensing voltage and the input voltage satisfy a firstcondition so that the bleeder does not generate a second current, andgenerating the control signal to turn on the bleeder if the sensingsignal and the input voltage satisfy a second condition so that thebleeder generates the second current. The second current is larger thanzero in magnitude. The second condition is different from the firstcondition.

According to certain embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving a sensing voltage, the sensing voltageindicating a magnitude of the first current, receiving an input voltage,the input voltage indicating a magnitude of the rectified voltage, andoutputting a control signal to the bleeder. The outputting a controlsignal to the bleeder includes generating the control signal to turn offthe bleeder if the input voltage satisfies a first condition so that thebleeder does not generate a second current, and generating the controlsignal to turn on the bleeder if the input voltage satisfies a secondcondition so that the bleeder generates the second current. The secondcurrent is larger than zero in magnitude. The second condition isdifferent from the first condition.

According to some embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving a sensing voltage, the sensing voltageindicating a magnitude of the first current, receiving an input voltage,the input voltage indicating a magnitude of a dimmer output voltagegenerated by the TRIAC dimmer and received by the rectifying bridge, andoutputting a control signal to the bleeder. The outputting a controlsignal to the bleeder includes generating the control signal to turn offthe bleeder if the sensing voltage and the input voltage satisfy a firstcondition so that the bleeder does not generate a second current, andgenerating the control signal to turn on the bleeder if the sensingsignal and the input voltage satisfy a second condition so that thebleeder generates the second current. The second current is larger thanzero in magnitude. The second condition is different from the firstcondition.

According to certain embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving a sensing voltage; receiving an input voltage,and outputting a control signal to the bleeder. The sensing voltageindicates a magnitude of the first current, and the input voltageindicates a magnitude of a dimmer output voltage generated by the TRIACdimmer and received by the rectifying bridge. The outputting a controlsignal to the bleeder includes generating the control signal to turn offthe bleeder if the input voltage satisfies a first condition so that thebleeder does not generate a second current, and generating the controlsignal to turn on the bleeder if the input voltage satisfies a secondcondition so that the bleeder generates the second current. The secondcurrent is larger than zero in magnitude. The second condition isdifferent from the first condition.

4. BRIEF DESCRIPTION OF THE DRAWINGS

According to various examples, other features, purposes, and advantagesof the present invention will become apparent upon reading the detaileddescription of the following exemplary drawings, which describe featuresof one or more non-limiting embodiments. For example, the same orsimilar reference numerals indicate the same or similar features.

FIG. 1 is an exemplary circuit diagram showing a conventional linearconstant current LED lighting system 100 with a TRIAC dimmer.

FIG. 2 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to some embodiments of the presentinvention.

FIG. 3 shows simplified timing diagrams for controlling the LED lightingsystem as shown in FIG. 2 according to one embodiment of the presentinvention.

FIG. 4 is a simplified circuit diagram showing a bleeder control unit ofan LED lighting system with a TRIAC dimmer (e.g., the bleeder controlunit of the LED lighting system as shown in FIGS. 2 and 3 ) according toone embodiment of the present invention.

FIG. 5 shows simplified timing diagrams for controlling the LED lightingsystem as shown in FIG. 2 according to another embodiment of the presentinvention.

FIG. 6 is a simplified circuit diagram showing a bleeder control unit ofan LED lighting system with a TRIAC dimmer (e.g., the bleeder controlunit of the LED lighting system as shown in FIGS. 2 and 5 ) according toanother embodiment of the present invention.

FIG. 7 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to certain embodiments of the presentinvention.

FIG. 8 shows simplified timing diagrams for controlling the LED lightingsystem 700 as shown in FIG. 7 according to one embodiment of the presentinvention.

FIG. 9 is a simplified circuit diagram showing a bleeder control unit ofan LED lighting system with a TRIAC dimmer (e.g., the bleeder controlunit of the LED lighting system as shown in FIGS. 7 and 8 ) according toone embodiment of the present invention.

FIG. 10 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to some embodiments of the presentinvention.

5. DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention are directed to circuits.More particularly, some embodiments of the invention provide switchcontrol systems for light emitting diodes (LEDs). Merely by way ofexample, some embodiments of the invention have been applied to LEDlighting systems. But it would be recognized that the invention has amuch broader range of applicability.

FIG. 2 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to some embodiments of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 2 , the controller of the system 200 includes a constant current(CC) unit 210 (e.g., a current generator), a bleeder unit 220 (e.g., ableeder), and a bleeder control unit 230 (e.g., a controller). In someexamples, the system 200 includes a line (L) terminal and a neutral (N)terminal. For example, an AC input voltage (e.g., VAC) is received by aTRIAC dimmer 290 and also rectified (e.g., by a full wave rectifyingbridge 292) to generate a rectified voltage 201 (e.g., VIN). As anexample, the full wave rectifying bridge 292 is coupled to the TRIACdimmer 290 through a fuse. For example, the rectified voltage 201 doesnot fall below the ground voltage of the chip (e.g., zero volt). Incertain examples, the constant current unit 210 includes a transistor M1for power regulation, a sensing resistor R1, and an amplifier U1 (e.g.,an error amplifier). As an example, the source of the transistor M1 forpower regulation is connected to the sensing resistor R1, the gate ofthe transistor M1 for power regulation is connected to an outputterminal of the amplifier U1, and the drain of the transistor M1 forpower regulation is connected to a cathode of an LED. Although the abovehas been shown using a selected group of components for the LED lightingsystem, there can be many alternatives, modifications, and variations.For example, some of the components may be expanded and/or combined.Other components may be inserted to those noted above. Depending uponthe embodiment, the arrangement of components may be interchanged withothers replaced. Further details of these components are foundthroughout the present specification.

As shown in FIG. 2 , the bleeder unit 220 includes an amplifier 221(e.g., an error amplifier), a transistor M2 for power regulation, aresistor R2, and a switch SW1 according to certain embodiments. In someembodiments, one terminal of the resistor R2 is grounded, and anotherterminal of the resistor R2 is connected to the amplifier 221 to providea sensing voltage 204 as an input. In certain embodiments, the amplifier221 generates a signal 223 based on the sensing voltage 204 across theresistor R2 and a reference voltage V_(ref2), and outputs the signal 223to control the transistor M2 for power regulation if the switch SW1 isopen.

For example, if the switch SW1 is closed, the bleeder unit 220 is turnedoff and/or stops working (e.g., the bleeder current 280 being equal tozero in magnitude). As an example, if the switch SW1 is open, thebleeder unit 220 is turned on, generating the bleeder current (e.g.,I_(bleed)) as determined by Equation 5:I _(bleed) =V _(ref2) /R ₂  (Equation 5)where V_(ref2) represents the reference voltage received by theamplifier 221, and R₂ represents the resistance of the resistor R2.

According to some embodiments, the bleeder control unit 230 isconfigured to detect a change in a current 282 by receiving a sensingvoltage V_(sense) (e.g., a sensing voltage 202), and the current 282 isgenerated by the constant current unit 210. For example, the current 282(e.g., I_(led)) flows through the LED into the constant current unit210. As an example, the current 282 (e.g., I_(led)) flows through theresistor R1 to generate the sensing voltage V_(sense) (e.g., the sensingvoltage 202). In some examples, if the current 282 generated by theconstant current unit 210 satisfies a first condition (e.g., when thecurrent 282 is greater than a first threshold current), the bleedercontrol unit 230 (e.g., with or without a delay) turns off the bleederunit 220 so that the bleeder unit 220 stops generating the bleedercurrent 280 (e.g., the bleeder current 280 being equal to zero inmagnitude). For example, the bleeder control unit 230 is configured toturn off the bleeder unit 220 by enabling (e.g., by closing) the switchSW1. In certain examples, if the current 282 generated by the constantcurrent unit 210 does not satisfy the first condition, the bleedercontrol unit 230 (e.g., with or without a delay) turns on the bleederunit 220 so that the bleeder unit 220 generates the bleeder current 280(e.g., the bleeder current 280 being larger than zero in magnitude),enabling a TRIAC dimmer 290 to operate normally. For example, thebleeder control unit 230 is configured to turn on the bleeder unit 220by disabling (e.g., by opening) the switch SW1.

According to certain embodiments, the bleeder control unit 230 isconfigured to generate a control signal 232 to turn off the bleeder unit220 (e.g., with or without a delay) if the sensing voltage 202 satisfiesthe first condition (e.g., when the sensing voltage 202 is greater thana first threshold voltage). According to some embodiments, the bleedercontrol unit 230 is configured to generate the control signal 232 toturn on the bleeder unit 220 to generate the bleeder current 280 (e.g.,with or without a delay) if the sensing voltage 202 does not satisfy thefirst condition. For example, the bleeder control unit 230 includes acomparator that is configured to receive the sensing voltage 202 and thefirst threshold voltage in order to generate the control signal 232based on at least the sensing voltage 202 and the first thresholdvoltage.

In some embodiments, the constant current (CC) unit 210 samples the peakamplitude of the sensing voltage 202 during each AC cycle, and transmitsthe sampled peak amplitude to the amplifier U1 of the constant currentunit 210. As an example, the amplifier U1 of the constant current unit210 also receives a reference voltage V_(ref1) and processes the sensingvoltage 202 on a cycle-by-cycle basis.

In certain embodiments, as shown in FIG. 2 , the transistor M1 for powerregulation is a field effect transistor (e.g., ametal-oxide-semiconductor field effect transistor (MOSFET)). Forexample, the transistor M1 for power regulation is an insulated gatebipolar transistor (IGBT). As an example, the transistor M1 for powerregulation is a bipolar junction transistor. In some examples, thecontroller of the system 200 includes more or less components. Incertain examples, the value of a reference voltage (e.g., the referencevoltage V_(ref1) and/or the reference voltage V_(ref2)) can be set asdesired by those skilled in the art.

As discussed above and further emphasized here, FIG. 2 is merely anexample, which should not unduly limit the scope of the claims. Forexample, the system 200 is configured to provide dimming control to oneor more LEDs. As an example, multiple LEDs are connected in series.

FIG. 3 shows simplified timing diagrams for controlling the LED lightingsystem 200 as shown in FIG. 2 according to one embodiment of the presentinvention. These diagrams are merely examples, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The waveform310 represents the rectified voltage VIN (e.g., the rectified voltage201) as a function of time, the waveform 320 represents the LED currentI_(led) (e.g., the current 282) as a function of time, and the waveform330 represents the bleeder current I_(bleed) (e.g., the bleeder current280) as a function of time. According to some embodiments, the timeperiod from time t0 to time t3 represents a half cycle of the AC inputvoltage (e.g., VAC). For example, the time period from time t0 to timet3 is equal to half a period of the AC input voltage (e.g., VAC).According to certain embodiments, the time period from time t1 to timet4 represents a half cycle of the AC input voltage (e.g., VAC). As anexample, the time period from time t1 to time t4 is equal to half aperiod of the AC input voltage (e.g., VAC).

In some embodiments, from time t0 to time t1 (e.g., when the system 200operates normally and the AC input voltage is clipped by the TRIACdimmer 290), the rectified voltage 201 (e.g., VIN) is small in magnitude(e.g., close to 0V), and the constant current unit 210 is not able togenerate the current 282 (e.g., the current 282 being equal to zero inmagnitude). For example, from time t0 to time t1, the current 282 isequal to zero in magnitude due to the clipping effect of the TRIACdimmer 290 as shown by the waveforms 310 and 320. As an example, fromtime t0 to time t1, the bleeder unit 220 is turned-on, generating thebleeder current 280 (e.g., the bleeder current 280 being larger thanzero in magnitude), as shown by the waveform 330. In certainembodiments, from time t1 to time t3, the system 200 operates normallyand the AC input voltage (e.g., VAC) is not clipped by the TRIAC dimmer290. In some examples, from time t1 to time t2, the rectified voltage201 (e.g., VIN) is sufficiently large in magnitude, and the constantcurrent unit 210 is able to generate the current 282 (e.g., the current282 being larger than zero in magnitude) as shown by the waveforms 310and 320. For example, from time t1 to time t2, the current 282 is equalto a predetermined magnitude larger than zero as shown by the waveform320. As an example, from time t1 to time t2, the bleeder unit 220 isturned off, not generating the bleeder current 280 (e.g., the bleedercurrent 280 being equal to zero in magnitude), as shown by the waveform330. In certain examples, from time t2 to time t3, the rectified voltage201 (e.g., VIN) is not sufficiently large in magnitude, and the constantcurrent unit 210 is not able to generate the current 282 (e.g., thecurrent 282 being equal to zero in magnitude) as shown by the waveforms310 and 320. As an example, from time t2 to time t3, the bleeder unit220 is turned-on, generating the bleeder current 280 (e.g., the bleedercurrent 280 being larger than zero in magnitude), as shown by thewaveform 330. In some embodiments, from time t3 to time t4, the system200 operates normally and the AC input voltage (e.g., VAC) is clipped bythe TRIAC dimmer 290 as shown by the waveform 310. For example, fromtime t3 to time t4, the constant current unit 210 is unable to generatethe current 282 (e.g., the current 282 being equal to zero in magnitude)as shown by the waveform 320. As an example, from time t3 to time t4,the bleeder unit 220 is turned-on, generating the bleeder current 280(e.g., the bleeder current 280 being larger than zero in magnitude), asshown by the waveform 330.

In certain embodiments, the transistor M2 for power regulation is closed(e.g., being turned on) at a first time (e.g., time t0). For example,when the sensing voltage 202 is less than a first threshold voltage(e.g., V_(ref3)) (e.g., from time t0 to time t1), the control signal 232is at a first logic level (e.g., at a logic low level). As an example,when the sensing voltage 202 is greater than the first threshold voltage(e.g., V_(ref3)) (e.g., from time t1 to time t2), the control signal 232is at a second logic level (e.g., at a logic high level). For example,when the sensing voltage 202 is less than the first threshold voltage(e.g., V_(ref3)) (e.g., from time t2 to time t3), the control signal 232is at the first logic level (e.g., at the logic low level).

As shown in FIG. 2 , in some embodiments, if the switch SW1 is closed,the transistor M2 is turned off and the bleeder unit 220 is also turnedoff so that the bleeder current 280 is equal to zero in magnitude. Incertain embodiments, if the switch SW1 is open, the transistor M2 can beturned on by the signal 223 and the bleeder unit 220 is also turned onso that the bleeder current 280 is larger than zero in magnitude.

FIG. 4 is a simplified circuit diagram showing a bleeder control unit ofan LED lighting system with a TRIAC dimmer (e.g., the bleeder controlunit 230 of the LED lighting system 200 as shown in FIGS. 2 and 3 )according to one embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 4 , thebleeder control unit (e.g., the bleeder control unit 230) includes acomparator U301. In some examples, the comparator U301 receives areference voltage V_(ref3) and a sensing voltage V_(sense) (e.g., thesensing voltage 202), and outputs a bleeder control signal bleeder_off(e.g., the control signal 232). For example, if the bleeder controlsignal bleeder_off (e.g., the control signal 232) is at a logic highlevel, the switch SW1 is closed and the bleeder unit 220 is turned offso that the bleeder unit 220 does not generate the bleeder current 280(e.g., the bleeder current 280 being equal to zero in magnitude). As anexample, if the bleeder control signal bleeder_off (e.g., the controlsignal 232) is at a logic low level, the switch SW1 is open and thebleeder unit 220 is turned on so that the bleeder unit 220 generates thebleeder current 280 (e.g., the bleeder current 280 being larger thanzero in magnitude). In certain examples, the system 200 determines themagnitude of the current 282 by sensing the voltage V_(sense) across thesensing resistor R1 of the constant current unit 210 as shown in FIG. 2. Although the above has been shown using a selected group of componentsfor the bleeder control unit, there can be many alternatives,modifications, and variations. For example, some of the components maybe expanded and/or combined. Other components may be inserted to thosenoted above. Depending upon the embodiment, the arrangement ofcomponents may be interchanged with others replaced. Further details ofthese components are found throughout the present specification.

In some embodiments, the comparator U301 compares the reference voltageV_(ref3) and the sensing voltage V_(sense) (e.g., the sensing voltage202). For example, if the current 282 generated by the constant currentunit 210 is greater than the holding current of the TRIAC dimmer 290,when the sensing voltage V_(sense) becomes larger than the referencevoltage V_(ref3) in magnitude, the comparator U301 generates the bleedercontrol signal bleeder_off (e.g., the control signal 232) at the logichigh level to turn off the bleeder unit 220 so that the bleeder current280 is equal to zero in magnitude. As an example, if the current 282generated by the constant current unit 210 is less than the holdingcurrent of the TRIAC dimmer 290, when the sensing voltage V_(sense) issmaller than the reference voltage V_(ref3) in magnitude, the comparatorU301 generates the bleeder control signal bleeder_off (e.g., the controlsignal 232) at the logic low level to turn on the bleeder unit 220 sothat the bleeder current 280 is larger than zero in magnitude. Incertain examples, the LED lighting system 200 that includes the bleedercontrol unit 230 as shown in FIG. 4 operates according to FIG. 3 . Insome examples, the reference voltage V_(ref3) is smaller than thereference voltage V_(ref1) of the constant current unit 210.

As discussed above and further emphasized here, FIG. 3 shows merelyexamples, which should not unduly limit the scope of the claims. In someexamples, the TRIAC dimmer 290 needs the current that flows through theTRIAC dimmer 290 to not fall below a holding current during the timeduration when the constant current unit 210 is supposed to generate thecurrent 282 (e.g., the current 282 being larger than zero in magnitude)under normal operation. For example, if the current that flows throughthe TRIAC dimmer 290 falls below the holding current, the TRIAC dimmer290 may misfire, causing the constant current unit 210 to operateabnormally. In certain examples, when the constant current unit 210 isnot supposed to generate the current 282 (e.g., the current 282 beinglarger than zero in magnitude) under normal operation, if the currentthat flows through the TRIAC dimmer 290 falls below the holding current,luminance of the one or more LEDs of the system 200 would not beaffected.

FIG. 5 shows simplified timing diagrams for controlling the LED lightingsystem 200 as shown in FIG. 2 according to another embodiment of thepresent invention. These diagrams are merely examples, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thewaveform 510 represents the rectified voltage VIN (e.g., the rectifiedvoltage 201) as a function of time, the waveform 520 represents the LEDcurrent I_(led) (e.g., the current 282) as a function of time, and thewaveform 530 represents the bleeder current I_(bleed) (e.g., the bleedercurrent 280) as a function of time. According to some embodiments, thetime period from time t0 to time t4 represents a half cycle of the ACinput voltage (e.g., VAC). For example, the time period from time t0 totime t4 is equal to half a period of the AC input voltage (e.g., VAC).According to certain embodiments, the time period from time t1 to timet5 represents a half cycle of the AC input voltage (e.g., VAC). As anexample, the time period from time t1 to time t5 is equal to half aperiod of the AC input voltage (e.g., VAC).

In some embodiments, from time t0 to time t1 (e.g., when the system 200operates normally and the AC input voltage is clipped by the TRIACdimmer 290), the rectified voltage 201 (e.g., VIN) is small in magnitude(e.g., close to 0V), and the constant current unit 210 is not able togenerate the current 282 (e.g., the current 282 being equal to zero inmagnitude). For example, from time t0 to time t1, the current 282 isequal to zero in magnitude due to the clipping effect of the TRIACdimmer 290 as shown by the waveforms 510 and 520. As an example, fromtime t0 to time t1, the bleeder unit 220 is turned-on, generating thebleeder current 280 (e.g., the bleeder current 280 being larger thanzero in magnitude), as shown by the waveform 530. In certainembodiments, from time t1 to time t4, the system 200 operates normallyand the AC input voltage (e.g., VAC) is not clipped by the TRIAC dimmer290. In some examples, from time t1 to time t2, the rectified voltage201 (e.g., VIN) is sufficiently large in magnitude, and the constantcurrent unit 210 is able to generate the current 282 (e.g., the current282 being larger than zero in magnitude) as shown by the waveforms 510and 520. For example, from time t1 to time t2, the current 282 is equalto a predetermined magnitude larger than zero as shown by the waveform520. As an example, from time t1 to time t2, the bleeder unit 220 isturned off, not generating the bleeder current 280 (e.g., the bleedercurrent 280 being equal to zero in magnitude), as shown by the waveform530. In certain examples, from time t2 to time t3, the rectified voltage201 (e.g., VIN) is not sufficiently large in magnitude, and the constantcurrent unit 210 is not able to generate the current 282 (e.g., thecurrent 282 being equal to zero in magnitude) as shown by the waveforms510 and 520. As an example, from time t2 to time t3, the bleeder unit220 remains turned off, not generating the bleeder current 280 (e.g.,the bleeder current 280 being equal to zero in magnitude), as shown bythe waveform 530. For example, the time duration from time t2 to time t3is represented by a constant delay td (e.g., a predetermined delay timeduration). As an example, from time t2 to time t3, the bleeder current280 remains equal to zero in magnitude to reduce the power consumptionof the bleeder current 280.

In some examples, from time t3 to time t4, the rectified voltage 201(e.g., VIN) remains not sufficiently large in magnitude, and theconstant current unit 210 remains not able to generate the current 282(e.g., the current 282 being equal to zero in magnitude) as shown by thewaveforms 510 and 520. As an example, from time t3 to time t4, thebleeder unit 220 is turned-on, generating the bleeder current 280 (e.g.,the bleeder current 280 being larger than zero in magnitude), as shownby the waveform 530. For example, the rectified voltage 201 (e.g., VIN)from time t3 to time t4 is smaller than the rectified voltage 201 (e.g.,VIN) from time t2 to time t3, so the power consumption by the non-zerobleeder current 280 from time t3 to time t4 is also smaller than thepower consumption of the bleeder current 280 from time t2 to time t3 ifthe same non-zero bleeder current 280 were generated from time t2 totime t3. In some embodiments, from time t4 to time t5, the system 200operates normally and the AC input voltage (e.g., VAC) is clipped by theTRIAC dimmer 290 as shown by the waveform 510. For example, from time t4to time t5, the constant current unit 210 is unable to generate thecurrent 282 (e.g., the current 282 being equal to zero in magnitude), asshown by the waveform 520. As an example, from time t4 to time t5, thebleeder unit 220 is turned-on, generating the bleeder current 280 (e.g.,the bleeder current 280 being larger than zero in magnitude), as shownby the waveform 530.

FIG. 6 is a simplified circuit diagram showing a bleeder control unit ofan LED lighting system with a TRIAC dimmer (e.g., the bleeder controlunit 230 of the LED lighting system 200 as shown in FIGS. 2 and 5 )according to another embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 6 , thebleeder control unit (e.g., the bleeder control unit 230) includes acomparator U301 and a delay circuit U302. In some examples, thecomparator U301 receives a reference voltage V_(ref3) and a sensingvoltage V_(sense) (e.g., the sensing voltage 202) and outputs acomparison signal 602 to the delay circuit U302, and in response, thedelay circuit U302 generates and outputs a bleeder control signalbleeder_off (e.g., the control signal 232). For example, if the bleedercontrol signal bleeder_off (e.g., the control signal 232) is at a logichigh level, the switch SW1 is closed and the bleeder unit 220 is turnedoff so that the bleeder unit 220 does not generate the bleeder current280 (e.g., the bleeder current 280 being equal to zero in magnitude). Asan example, if the bleeder control signal bleeder_off (e.g., the controlsignal 232) is at a logic low level, the switch SW1 is open and thebleeder unit 220 is turned on so that the bleeder unit 220 generates thebleeder current 280 (e.g., the bleeder current 280 being larger thanzero in magnitude). In certain examples, the system 200 determines themagnitude of the current 282 by sensing the voltage V_(sense) across thesensing resistor R1 of the constant current unit 210 as shown in FIG. 2. Although the above has been shown using a selected group of componentsfor the bleeder control unit, there can be many alternatives,modifications, and variations. For example, some of the components maybe expanded and/or combined. Other components may be inserted to thosenoted above. Depending upon the embodiment, the arrangement ofcomponents may be interchanged with others replaced. Further details ofthese components are found throughout the present specification.

In some embodiments, the comparator U301 compares the reference voltageV_(ref3) and the sensing voltage V_(sense). For example, if the current282 generated by the constant current unit 210 is greater than theholding current of the TRIAC dimmer 290, when V_(sense) becomes largerthan V_(ref3) in magnitude, the delay circuit U302 generates the bleedercontrol signal bleeder_off (e.g., the control signal 232) at the logichigh level to turn off the bleeder unit 220 so that the bleeder current280 is equal to zero in magnitude. As an example, if the current 282generated by the constant current unit 210 is less than the holdingcurrent of the TRIAC dimmer 290, when V_(sense) becomes smaller thanV_(ref3) in magnitude, the delay circuit U302, after the constant delaytd (e.g., a predetermined delay time duration), generates the bleedercontrol signal bleeder_off (e.g., the control signal 232) at the logiclow level to turn on the bleeder unit 220 so that the bleeder current280 is larger than zero in magnitude. In certain examples, the LEDlighting system 200 that includes the bleeder control unit 230 as shownin FIG. 6 operates according to FIG. 5 . In some examples, the referencevoltage V_(ref3) is smaller than the reference voltage V_(ref1) of theconstant current unit 210.

As shown in FIG. 6 , the bleeder control unit (e.g., the bleeder controlunit 230) includes the comparator U301 and the delay circuit U302. Insome examples, the delay circuit U302 does not provide any delay if thecomparison signal 602 changes from the logic low to the logic high levelso that the bleeder current 280 becomes zero in magnitude without delay(e.g., at time t1 and/or at time t5 as shown in FIG. 5 ). In certainexamples, the delay circuit U302 provides a delay if the comparisonsignal 602 changes from the logic high to the logic low level so thatthe bleeder current 280 becomes larger than zero in magnitude afterdelay (e.g., at time t3 after a predetermined delay time duration asshown in FIG. 5 ). For example, the delay circuit U302 is configured toprovide the predetermined delay time duration (e.g., the constant delaytd), so that as shown in FIG. 5 , from time t2 to time t3, the bleedercontrol signal bleeder_off (e.g., the control signal 232) remains at thelogic high level and the bleeder current 280 remains equal to zero inmagnitude.

As discussed above and further emphasized here, FIGS. 2 and 5 are merelyexamples, which should not unduly limit the scope of the claims. In someexamples, the time duration from time t2 to time t3 (e.g., a delay td)is not a predetermined constant. In certain examples, the time durationfrom time t2 to time t3 (e.g., a delay td) is determined by detectingthe input voltage VIN.

FIG. 7 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to certain embodiments of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 7 , the controller of the system 700 includes a constant current(CC) unit 710 (e.g., a current generator), a bleeder unit 720 (e.g., ableeder), and a bleeder control unit 730 (e.g., a controller). In someexamples, the system 700 includes a line (L) terminal and a neutral (N)terminal. For example, an AC input voltage (e.g., VAC) is received by aTRIAC dimmer 790 and also rectified (e.g., by a full wave rectifyingbridge 792) to generate a rectified voltage 701 (e.g., VIN). As anexample, the full wave rectifying bridge 792 is coupled to the TRIACdimmer 790 through a fuse. For example, the rectified voltage 701 doesnot fall below the ground voltage of the chip (e.g., zero volt). Incertain examples, the constant current unit 710 includes a transistor M1for power regulation, a sensing resistor R1, and an amplifier U1 (e.g.,an error amplifier). As an example, the source of the transistor M1 forpower regulation is connected to the sensing resistor R1, the gate ofthe transistor M1 for power regulation is connected to an outputterminal of the amplifier U1, and the drain of the transistor M1 forpower regulation is connected to a cathode of an LED. Although the abovehas been shown using a selected group of components for the LED lightingsystem, there can be many alternatives, modifications, and variations.For example, some of the components may be expanded and/or combined.Other components may be inserted to those noted above. Depending uponthe embodiment, the arrangement of components may be interchanged withothers replaced. Further details of these components are foundthroughout the present specification.

As shown in FIG. 7 , the bleeder unit 720 includes an amplifier 721(e.g., an error amplifier), a transistor M2 for power regulation, aresistor R2, and a switch SW1 according to certain embodiments. In someembodiments, one terminal of the resistor R2 is grounded, and anotherterminal of the resistor R2 is connected to the amplifier 721 to providea sensing voltage 704 as an input. In certain embodiments, the amplifier721 generates a signal 723 based on the sensing voltage 704 across theresistor R2 and a reference voltage V_(ref2), and outputs the signal 723to control the transistor M2 for power regulation if the switch SW1 isopen.

For example, if the switch SW1 is closed, the bleeder unit 720 is turnedoff and/or stops working (e.g., the bleeder current 780 being equal tozero in magnitude). As an example, if the switch SW1 is open, thebleeder unit 720 is turned on, generating the bleeder current (e.g.,I_(bleed)) as determined by Equation 6:I _(bleed) =V _(ref2) /R ₂  (Equation 6)where V_(ref2) represents the reference voltage received by theamplifier 721, and R₂ represents the resistance of the resistor R2.

According to some embodiments, the bleeder control unit 730 isconfigured to detect a change in a current 782 by receiving a sensingvoltage V_(sense) (e.g., a sensing voltage 702), and the current 782 isgenerated by the constant current unit 710. In some examples, thebleeder control unit 730 also includes an input terminal LS forreceiving a voltage 734 generated by a voltage divider. For example, thevoltage divider includes resistors R3 and R5 and is biased between therectified voltage VIN (e.g., the rectified voltage 701) and the groundvoltage, where one terminal of the resistor R3 is biased at therectified voltage VIN and one terminal of the resistor R5 is biased atthe ground voltage. As an example, the bleeder control unit 730 isfurther configured to detect a change in the rectified voltage VIN(e.g., the rectified voltage 701) by sensing the voltage 734. In certainexamples, the current 782 (e.g., I_(led)) flows through the LED and intothe constant current unit 710.

In certain examples, if the current 782 generated by the constantcurrent unit 710 satisfies a first condition (e.g., when the current 782is greater than a first threshold current), the bleeder control unit 730(e.g., with or without a delay) turns off the bleeder unit 720 so thatthe bleeder unit 720 stops generating the bleeder current 780 (e.g., thebleeder current 780 being equal to zero in magnitude). For example, thebleeder control unit 730 is configured to turn off the bleeder unit 720by enabling (e.g., by closing) the switch SW1. In some examples, if thecurrent 782 generated by the constant current unit 710 does not satisfythe first condition but the rectified voltage VIN (e.g., the rectifiedvoltage 701) satisfies a second condition (e.g., when the rectifiedvoltage 701 is greater than a second threshold voltage), the bleedercontrol unit 730 (e.g., with or without a delay) still turns off thebleeder unit 720 so that the bleeder unit 720 still does not generatethe bleeder current 780 (e.g., the bleeder current 780 being equal tozero in magnitude). In certain examples, if the current 782 generated bythe constant current unit 710 does not satisfy the first condition andthe rectified voltage VIN (e.g., the rectified voltage 701) does notsatisfy the second condition, the bleeder control unit 230 (e.g., withor without a delay) turns on the bleeder unit 720 so that the bleederunit 720 generates the bleeder current 780 (e.g., the bleeder current780 being larger than zero in magnitude), enabling a TRIAC dimmer 790 tooperate normally. For example, the bleeder control unit 730 isconfigured to turn on the bleeder unit 720 by disabling (e.g., byopening) the switch SW1.

According to certain embodiments, the bleeder control unit 730 isconfigured to generate a control signal 732 to turn off the bleeder unit720 (e.g., with or without a delay) if the sensing voltage 702 satisfiesthe first condition (e.g., when the sensing voltage 702 is greater thana first threshold voltage). According to some embodiments, the bleedercontrol unit 730 is configured to generate the control signal 732 toturn on the bleeder unit 720 to generate the current 780 (e.g., with orwithout a delay) if the sensing voltage 702 does not satisfy the firstcondition and the rectified voltage VIN (e.g., the rectified voltage701) does not satisfy the second condition (e.g., the second conditionbeing satisfied when the rectified voltage 701 is greater than a secondthreshold voltage).

In some embodiments, the constant current (CC) unit 710 samples the peakamplitude of the sensing voltage 702 during each AC cycle, and transmitsthe sampled peak amplitude to the amplifier U1 of the constant currentunit 710. As an example, the amplifier U1 of the constant current unit710 also receives a reference voltage V_(ref1) and processes the sensingvoltage 702 on a cycle-by-cycle basis.

In certain embodiments, as shown in FIG. 7 , the transistor M1 for powerregulation is a field effect transistor (e.g., ametal-oxide-semiconductor field effect transistor (MOSFET)). Forexample, the transistor M1 for power regulation is an insulated gatebipolar transistor (IGBT). As an example, the transistor M1 for powerregulation is a bipolar junction transistor. In some examples, thecontroller of the system 200 includes more or less components. Incertain examples, the value of a reference voltage (e.g., the referencevoltage V_(ref1) and/or the reference voltage V_(ref2)) can be set asdesired by those skilled in the art.

As discussed above and further emphasized here, FIG. 7 is merely anexample, which should not unduly limit the scope of the claims. Forexample, the system 700 is configured to provide dimming control to oneor more LEDs. As an example, multiple LEDs are connected in series.

FIG. 8 shows simplified timing diagrams for controlling the LED lightingsystem 700 as shown in FIG. 7 according to one embodiment of the presentinvention. These diagrams are merely examples, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The waveform810 represents the rectified voltage VIN (e.g., the rectified voltage701) as a function of time, the waveform 820 represents the LED currentI_(led) (e.g., the current 782) as a function of time, and the waveform830 represents the bleeder current I_(bleed) (e.g., the bleeder current780) as a function of time. According to some embodiments, the timeperiod from time t0 to time t4 represents a half cycle of the AC inputvoltage (e.g., VAC). For example, the time period from time t0 to timet4 is equal to half a period of the AC input voltage (e.g., VAC).According to certain embodiments, the time period from time t1 to timet5 represents a half cycle of the AC input voltage (e.g., VAC). As anexample, the time period from time t1 to time t5 is equal to half aperiod of the AC input voltage (e.g., VAC).

In some embodiments, from time t0 to time t1 (e.g., when the system 700operates normally and the AC input voltage is clipped by the TRIACdimmer 790), the rectified voltage 701 (e.g., VIN) is small in magnitude(e.g., close to 0V), and the constant current unit 710 is not able togenerate the current 782 (e.g., the current 782 being equal to zero inmagnitude). For example, from time t0 to time t1, the current 782 isequal to zero in magnitude due to the clipping effect of the TRIACdimmer 790 as shown by the waveforms 810 and 820. As an example, fromtime t0 to time t1, the bleeder unit 720 is turned-on, generating thebleeder current 780 (e.g., the bleeder current 780 being larger thanzero in magnitude), as shown by the waveform 830. In certainembodiments, from time t1 to time t4, the system 700 operates normallyand the AC input voltage (e.g., VAC) is not clipped by the TRIAC dimmer790. In some examples, from time t1 to time t2, the rectified voltage701 (e.g., VIN) is sufficiently large in magnitude, and the constantcurrent unit 710 is able to generate the current 782 (e.g., the current782 being larger than zero in magnitude) as shown by the waveforms 810and 820. For example, from time t1 to time t2, the current 782 is equalto a predetermined magnitude larger than zero as shown by the waveform820. As an example, from time t1 to time t2, the bleeder unit 720 isturned off, not generating the bleeder current 780 (e.g., the bleedercurrent 780 being equal to zero in magnitude), as shown by the waveform830.

According to some embodiments, from time t2 to time t4, the rectifiedvoltage 701 (e.g., VIN) is not sufficiently large in magnitude, and theconstant current unit 710 is not able to generate the current 782 (e.g.,the current 782 being equal to zero in magnitude) as shown by thewaveforms 810 and 820. For example, at time t3, the rectified voltage701 (e.g., VIN) becomes smaller than a threshold voltage (e.g., V_(th)).In some examples, from time t2 to time t3, the bleeder unit 720 remainsturned off, not generating the bleeder current 780 (e.g., the bleedercurrent 780 being equal to zero in magnitude), as shown by the waveform830. For example, the time duration from time t2 to time t3 isrepresented by a delay td (e.g., not a predetermined constant). As anexample, from time t2 to time t3, the bleeder current 780 remains equalto zero in magnitude to reduce the power consumption of the bleedercurrent 280. In certain examples, from time t3 to time t4, the rectifiedvoltage 701 (e.g., VIN) remains not sufficiently large in magnitude, andthe constant current unit 710 remains not able to generate the current782 (e.g., the current 782 being equal to zero in magnitude) as shown bythe waveforms 810 and 820. As an example, from time t3 to time t4, thebleeder unit 720 is turned-on, generating the bleeder current 780 (e.g.,the bleeder current 780 being larger than zero in magnitude), as shownby the waveform 830. For example, the rectified voltage 701 (e.g., VIN)from time t3 to time t4 is smaller than the rectified voltage 701 (e.g.,VIN) from time t2 to time t3, so the power consumption by the non-zerobleeder current 780 from time t3 to time t4 is also smaller than thepower consumption of the bleeder current 780 from time t2 to time t3 ifthe same non-zero bleeder current 780 were generated from time t2 totime t3.

According to certain embodiments, from time t4 to time t5, the system700 operates normally and the AC input voltage (e.g., VAC) is clipped bythe TRIAC dimmer 790 as shown by the waveform 810. For example, fromtime t4 to time t5, the constant current unit 710 is unable to generatethe current 782 (e.g., the current 782 being equal to zero inmagnitude), as shown by the waveform 820. As an example, from time t4 totime t5, the bleeder unit 720 is turned-on, generating the bleedercurrent 780 (e.g., the bleeder current 780 being larger than zero inmagnitude), as shown by the waveform 830.

FIG. 9 is a simplified circuit diagram showing a bleeder control unit ofan LED lighting system with a TRIAC dimmer (e.g., the bleeder controlunit 730 of the LED lighting system 700 as shown in FIGS. 7 and 8 )according to one embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 9 , thebleeder control unit (e.g., the bleeder control unit 730) includescomparators U301 and U302 and a flip-flop U303.

In some examples, the comparator U301 receives a reference voltageV_(ref3) and a sensing voltage V_(sense) (e.g., the sensing voltage 702)and outputs a comparison signal 902, and the comparator U302 receivesthe voltage 734 and a reference voltage V_(ref4) and outputs acomparison signal 904. For example, the voltage 734 represents therectified voltage 701 (e.g., the voltage 734 being equal to therectified voltage 701 multiplied by a constant), and the referencevoltage V_(ref4) represents the threshold voltage (e.g., V_(th)) asshown in FIG. 8 . As an example, if the voltage 734 becomes larger thanthe reference voltage V_(ref4), the rectified voltage 701 becomes largerthan the threshold voltage (e.g., V_(th)). For example, if the voltage734 becomes smaller than the reference voltage V_(ref4), the rectifiedvoltage 701 becomes smaller than the threshold voltage (e.g., V_(th)).In certain examples, the flip-flop U303 receives the comparison signals902 and 904, and in response, generates and outputs a bleeder controlsignal bleeder_off (e.g., the control signal 732). For example, if thebleeder control signal bleeder_off (e.g., the control signal 732) is ata logic high level, the switch SW1 is closed and the bleeder unit 720 isturned off so that the bleeder unit 720 does not generate the bleedercurrent 780 (e.g., the bleeder current 780 being equal to zero inmagnitude). As an example, if the bleeder control signal bleeder_off(e.g., the control signal 732) is at a logic low level, the switch SW1is open and the bleeder unit 720 is turned on so that the bleeder unit720 generates the bleeder current 780 (e.g., the bleeder current 780being larger than zero in magnitude). In some examples, the system 700determines the magnitude of the current 782 by sensing the voltageV_(sense) across the sensing resistor R1 of the constant current unit710 as shown in FIG. 7 . Although the above has been shown using aselected group of components for the bleeder control unit, there can bemany alternatives, modifications, and variations. For example, some ofthe components may be expanded and/or combined. Other components may beinserted to those noted above. Depending upon the embodiment, thearrangement of components may be interchanged with others replaced.Further details of these components are found throughout the presentspecification.

In some embodiments, the comparator U301 compares the reference voltageV_(ref3) and the sensing voltage V_(sense) (e.g., the sensing voltage702). For example, if the current 782 generated by the constant currentunit 710 is greater than the holding current of the TRIAC dimmer 790,when the sensing voltage V_(sense) becomes larger than the referencevoltage V_(ref3) in magnitude, the flip-flop U303 generates the bleedercontrol signal bleeder off (e.g., the control signal 732) at the logichigh level to turn off the bleeder unit 720 so that the bleeder current780 is equal to zero in magnitude. As an example, if the current 782generated by the constant current unit 710 is less than the holdingcurrent of the TRIAC dimmer 790, when the sensing voltage V_(sense) issmaller than the reference voltage V_(ref3) in magnitude and the voltage734 becomes smaller than the reference voltage V_(ref4) in magnitude,the flip-flop U303 generates the bleeder control signal bleeder_off(e.g., the control signal 732) at the logic low level to turn on thebleeder unit 720 so that the bleeder current 780 is larger than zero inmagnitude.

In some examples, the LED lighting system 700 that includes the bleedercontrol unit 730 as shown in FIG. 9 operates according to FIG. 8 . Incertain examples, the reference voltage V_(ref3) is smaller than thereference voltage V_(ref1) of the constant current unit 710.

As shown in FIG. 9 , in certain embodiments, when the voltage 734becomes smaller than the reference voltage V_(ref4) in magnitude, theflip-flop U303 generates the bleeder control signal bleeder_off (e.g.,the control signal 732) at the logic low level to turn on the bleederunit 720 so that the bleeder current 780 is larger than zero inmagnitude.

As discussed above and further emphasized here, FIGS. 7 and 8 are merelyexamples, which should not unduly limit the scope of the claims. In someembodiments, the time duration from time t2 to time t3 (e.g., a delaytd) is not a predetermined constant. In certain embodiments, the timeduration from time t2 to time t3 (e.g., a delay td) is determined bydetecting a voltage generated by the TRIAC dimmer before being processedby the full wave rectifying bridge, as shown, for example, by FIG. 10 .

FIG. 10 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to some embodiments of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 10 , the controller of the system 1000 includes a constant current(CC) unit 1010 (e.g., a current generator), a bleeder unit 1020 (e.g., ableeder), and a bleeder control unit 1030 (e.g., a controller). In someexamples, the system 1000 includes a line (L) terminal and a neutral (N)terminal. For example, an AC input voltage (e.g., VAC) is received by aTRIAC dimmer 1090, which generates a voltage 1094 (e.g., the TRIACdimmer 1090 generating the voltage 1094 through a fuse). As an example,the voltage 1094 is rectified (e.g., by a full wave rectifying bridge1092) to generate a rectified voltage 1001 (e.g., VIN). For example, thefull wave rectifying bridge 1092 is coupled to the TRIAC dimmer 1090through a fuse. As an example, the rectified voltage 1001 does not fallbelow the ground voltage of the chip (e.g., zero volt). In certainexamples, the constant current unit 1010 includes a transistor M1 forpower regulation, a sensing resistor R1, and an amplifier U1 (e.g., anerror amplifier). For example, the source of the transistor M1 for powerregulation is connected to the sensing resistor R1, the gate of thetransistor M1 for power regulation is connected to an output terminal ofthe amplifier U1, and the drain of the transistor M1 for powerregulation is connected to a cathode of an LED. Although the above hasbeen shown using a selected group of components for the LED lightingsystem, there can be many alternatives, modifications, and variations.For example, some of the components may be expanded and/or combined.Other components may be inserted to those noted above. Depending uponthe embodiment, the arrangement of components may be interchanged withothers replaced. Further details of these components are foundthroughout the present specification.

As shown in FIG. 10 , the bleeder unit 1020 includes an amplifier 1021(e.g., an error amplifier), a transistor M2 for power regulation, aresistor R2, and a switch SW1 according to certain embodiments. In someembodiments, one terminal of the resistor R2 is grounded, and anotherterminal of the resistor R2 is connected to the amplifier 1021 toprovide a sensing voltage 1004 as an input. In certain embodiments, theamplifier 1021 generates a signal 1023 based on the sensing voltage 1004across the resistor R2 and a reference voltage V_(ref2), and outputs thesignal 1023 to control the transistor M2 for power regulation if theswitch SW1 is open.

For example, if the switch SW1 is closed, the bleeder unit 1020 isturned off and/or stops working (e.g., the bleeder current 1080 beingequal to zero in magnitude). As an example, if the switch SW1 is open,the bleeder unit 1020 is turned on, generating the bleeder current(e.g., bleed) as determined by Equation 7:I _(bleed) =V _(ref2) /R ₂  (Equation 7)where V_(ref2) represents the reference voltage received by theamplifier 1021, and R₂ represents the resistance of the resistor R2.

According to some embodiments, the bleeder control unit 1030 isconfigured to detect a change in a current 1082 by receiving a sensingvoltage V_(sense) (e.g., a sensing voltage 1002), and the current 1082is generated by the constant current unit 1010. In some examples, thebleeder control unit 1030 also includes an input terminal LS forreceiving a voltage 1034 generated by a combination of resistors R3, R4,and R5. For example, the resistors R3, R4, and R5 are parts of a voltagedivider. As an example, the resistor R3 is configured to receive thevoltage 1094, and another terminal of the resistor R3 is connected toone terminal of the resistor R4 and one terminal of the resistor R5. Forexample, the one terminal of the resistor R5 is configured to providethe voltage 1034. As an example, another terminal of the resistor R5 isbiased to the ground voltage, and another terminal of the resistor R4 isconnected to the N terminal of the system 1000. In certain examples, thebleeder control unit 1030 is further configured to detect a change inthe voltage 1094 by sensing the voltage 1034. In some examples, thecurrent 1082 (e.g., lied) flows through the LED into the constantcurrent unit 1010.

In certain examples, if the current 1082 generated by the constantcurrent unit 1010 satisfies a first condition (e.g., when the current1082 is greater than a first threshold current), the bleeder controlunit 1030 (e.g., with or without a delay) turns off the bleeder unit1020 so that the bleeder unit 1020 stops generating the bleeder current1080 (e.g., the bleeder current 1080 being equal to zero in magnitude).For example, the bleeder control unit 1030 is configured to turn off thebleeder unit 1020 by enabling (e.g., by closing) the switch SW1. In someexamples, if the current 1082 generated by the constant current unit1010 does not satisfy the first condition but the voltage 1094 satisfiesa second condition (e.g., when the voltage 1094 is greater than a secondthreshold voltage), the bleeder control unit 1030 (e.g., with or withouta delay) still turns off the bleeder unit 1020 so that the bleeder unit1020 still does not generate the bleeder current 1080 (e.g., the bleedercurrent 1080 being equal to zero in magnitude). In certain examples, ifthe current 1082 generated by the constant current unit 1010 does notsatisfy the first condition and the voltage 1094 does not satisfy thesecond condition, the bleeder control unit 1030 (e.g., with or without adelay) turns on the bleeder unit 1020 so that the bleeder unit 1020generates the bleeder current 1080 (e.g., the bleeder current 1080 beinglarger than zero in magnitude), enabling a TRIAC dimmer 1090 to operatenormally. For example, the bleeder control unit 1030 is configured toturn on the bleeder unit 1020 by disabling (e.g., by opening) the switchSW1.

According to certain embodiments, the bleeder control unit 1030 isconfigured to generate a control signal 1032 to turn off the bleederunit 1020 (e.g., with or without a delay) if the sensing voltage 1002satisfies the first condition (e.g., when the sensing voltage 1002 isgreater than a first threshold voltage). According to some embodiments,the bleeder control unit 1030 is configured to generate the controlsignal 1032 to turn on the bleeder unit 1020 to generate the current1080 (e.g., with or without a delay) if the sensing voltage 1002 doesnot satisfy the first condition and the voltage 1094 does not satisfythe second condition (e.g., the second condition being satisfied whenthe voltage 1094 is greater than a second threshold voltage).

In some embodiments, the constant current (CC) unit 1010 samples thepeak amplitude of the sensing voltage 1002 during each AC cycle, andtransmits the sampled peak amplitude to the amplifier U1 of the constantcurrent unit 1010. As an example, the amplifier U1 of the constantcurrent unit 1010 also receives a reference voltage V_(ref1) andprocesses the sensing voltage 1002 on a cycle-by-cycle basis.

In certain embodiments, as shown in FIG. 10 , the transistor M1 forpower regulation is a field effect transistor (e.g., ametal-oxide-semiconductor field effect transistor (MOSFET)). Forexample, the transistor M1 for power regulation is an insulated gatebipolar transistor (IGBT). As an example, the transistor M1 for powerregulation is a bipolar junction transistor. In some examples, thecontroller of the system 200 includes more or less components. Incertain examples, the value of a reference voltage (e.g., the referencevoltage V_(ref1) and/or the reference voltage V_(ref2)) can be set asdesired by those skilled in the art.

According to some embodiments, simplified timing diagrams forcontrolling the LED lighting system 1000 are shown in FIG. 8 , if thewaveform 810 represents the voltage 1094 as a function of time, thewaveform 820 represents the LED current I_(led) (e.g., the current 1082)as a function of time, and the waveform 830 represents the bleedercurrent I_(bleed) (e.g., the bleeder current 1080) as a function oftime. According to certain embodiments, the bleeder control unit 1030 ofthe LED lighting system 1000 is shown in FIG. 9 , where the comparatorU301 receives a reference voltage V_(ref3) and a sensing voltageV_(sense) (e.g., the sensing voltage 1002), the comparator U302 receivesthe voltage 1034 and a reference voltage V_(ref4), and the flip-flopU303 generates and outputs a bleeder control signal bleeder_off (e.g.,the control signal 1032).

As discussed above and further emphasized here, FIG. 10 is merely anexample, which should not unduly limit the scope of the claims. Forexample, the system 1000 is configured to provide dimming control to oneor more LEDs. As an example, multiple LEDs are connected in series.

In some embodiments, an LED switch control system includes a constantcurrent control unit, a bleeder unit, a bleeder control unit, and arectifier unit. For example, the constant current control unit iscoupled to a transistor and configured to output a first current. As anexample, the bleeder unit is coupled to a system input and the bleedercontrol unit. For example, the bleeder control unit is coupled to theconstant current control unit and the bleeder unit and configured toreceive a sensing signal. As an example, the rectifier unit isconfigured to rectify and filter an input voltage of the system andtransmit a rectified voltage to the bleeder unit and the constantcurrent control unit. For example, the bleeder control unit isconfigured to generate a control signal to disable the bleeder unit whenthe sensing signal satisfies a first condition and to generate thecontrol signal to enable the bleeder unit to output a bleeding currentwhen the sensing signal does not satisfy the first condition.

According to certain embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes are configured to receivea rectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator and output a control signalto the bleeder. The sensing voltage indicates a magnitude of the firstcurrent. The controller is further configured to generate the controlsignal to turn off the bleeder if the sensing voltage satisfies a firstcondition so that the bleeder does not generate a second current, andgenerate the control signal to turn on the bleeder if the sensing signalsatisfies a second condition so that the bleeder generates the secondcurrent. The second current is larger than zero in magnitude. The secondcondition is different from the first condition. For example, the systemis implemented according to at least FIG. 2 , FIG. 3 , FIG. 4 , FIG. 5 ,and/or FIG. 6 .

As an example, the first condition is the sensing voltage being largerthan a reference voltage in magnitude, and the second condition is thesensing voltage being smaller than the reference voltage in magnitude.For example, the controller includes a comparator configured to receivethe sensing voltage and a reference voltage, and the controller isfurther configured to change the control signal to turn off the bleederin response to the sensing voltage becoming larger than the referencevoltage in magnitude. As an example, the controller is furtherconfigured to change the control signal to turn on the bleeder inresponse to the sensing voltage becoming smaller than the referencevoltage in magnitude. For example, the controller is further configuredto change the control signal to turn on the bleeder, without a delay, inresponse to the sensing voltage becoming smaller than the referencevoltage in magnitude. As an example, the controller is furtherconfigured to change the control signal to turn on the bleeder, with adelay, in response to the sensing voltage becoming smaller than thereference voltage in magnitude. For example, the delay is apredetermined time duration. As an example, the delay is not apredetermined time duration.

For example, the controller is further configured to: generate thecontrol signal at a first logic level from a first time to a secondtime, during which the sensing voltage is smaller than a referencevoltage in magnitude; generate the control signal at a second logiclevel from the second time to a third time, during which the sensingvoltage is larger than the reference voltage in magnitude; and generatethe control signal at the first logic level from the third time to afourth time, during which the sensing voltage is smaller than thereference voltage in magnitude; wherein the first logic level and thesecond logic level are different. As an example, the control signal atthe first logic level is configured to turn on the bleeder so that thebleeder generates the second current, and the control signal at thesecond logic level is configured to turn off the bleeder so that thebleeder does not generate the second current.

For example, the controller includes a comparator configured to receivethe sensing voltage and a reference voltage and generate a comparisonsignal based at least in part on the sensing voltage and the referencevoltage, and a control signal generator configured to receive thecomparison and generate the control signal based at least in part on thecomparison signal. As an example, the control signal generator isfurther configured to change the control signal to turn on the bleeder,with a predetermined delay, in response to the sensing voltage becomingsmaller than the reference voltage in magnitude. For example, thecontroller is further configured to: generate the control signal at afirst logic level from a first time to a second time, during which thesensing voltage is smaller than the reference voltage in magnitude;generate the control signal at a second logic level from the second timeto a third time, during which the sensing voltage is larger than thereference voltage in magnitude; generate the control signal at thesecond logic level from the third time to a fourth time, during whichthe sensing voltage is smaller than the reference voltage in magnitude;and generate the control signal at the first logic level from the fourthtime to a fifth time, during which the sensing voltage is smaller thanthe reference voltage in magnitude; wherein: the first logic level andthe second logic level are different; and a time duration from the thirdtime to the fourth time is equal to the predetermined delay inmagnitude. As an example, the rectifying bridge is coupled to the TRIACdimmer through a fuse.

According to some embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes are configured to receivea rectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator, receive an input voltagegenerated by a voltage divider, and output a control signal to thebleeder. The sensing voltage indicates a magnitude of the first current,the voltage divider is configured to receive the rectified voltage, andthe input voltage indicates a magnitude of the rectified voltage. Thecontroller is further configured to generate the control signal to turnoff the bleeder if the sensing voltage and the input voltage satisfy afirst condition so that the bleeder does not generate a second current,and generate the control signal to turn on the bleeder if the sensingsignal and the input voltage satisfy a second condition so that thebleeder generates the second current. The second current is larger thanzero in magnitude. The second condition is different from the firstcondition. For example, the system is implemented according to at leastFIG. 7 , FIG. 8 , and/or FIG. 9 .

As an example, the voltage divider includes multiple resistors connectedin series and biased between the rectified voltage and a ground voltage.For example, the controller is further configured to: generate thecontrol signal at a first logic level from a first time to a secondtime, during which the sensing voltage is smaller than a first referencevoltage in magnitude and the input voltage is smaller than a secondreference voltage in magnitude; generate the control signal at a secondlogic level from the second time to a third time, during which thesensing voltage is larger than the first reference voltage in magnitudeand the input voltage is larger than the second reference voltage inmagnitude; generate the control signal at the second logic level fromthe third time to a fourth time, during which the sensing voltage issmaller than the first reference voltage in magnitude and the inputvoltage is larger than the second reference voltage in magnitude; andgenerate the control signal at the first logic level from the fourthtime to a fifth time, during which the sensing voltage is smaller thanthe first reference voltage in magnitude and the input voltage issmaller than the second reference voltage in magnitude; wherein thefirst logic level and the second logic level are different. As anexample, the controller is further configured to the control signal atthe first logic level is configured to turn on the bleeder so that thebleeder generates the second current, and the control signal at thesecond logic level is configured to turn off the bleeder so that thebleeder does not generate the second current. For example, therectifying bridge is coupled to the TRIAC dimmer through a fuse.

According to some embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes is configured to receive arectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator, the sensing voltageindicating a magnitude of the first current, receive an input voltagegenerated by a voltage divider, the voltage divider being configured toreceive the rectified voltage, the input voltage indicating a magnitudeof the rectified voltage, and output a control signal to the bleeder.The controller is further configured to generate the control signal toturn off the bleeder if the input voltage satisfies a first condition sothat the bleeder does not generate a second current, and generate thecontrol signal to turn on the bleeder if the input voltage satisfies asecond condition so that the bleeder generates the second current. Thesecond current is larger than zero in magnitude. The second condition isdifferent from the first condition. For example, the system isimplemented according to at least FIG. 7 , FIG. 8 , and/or FIG. 9 .

As an example, the controller is further configured to: generate thecontrol signal at a first logic level from a first time to a secondtime, during which the input voltage is smaller than a reference voltagein magnitude; generate the control signal at a second logic level fromthe second time to a third time, during which the input voltage islarger than the reference voltage in magnitude; and generate the controlsignal at the first logic level from the third time to a fourth time,during which the input voltage is smaller than the reference voltage inmagnitude; wherein the first logic level and the second logic level aredifferent. For example, the control signal at the first logic level isconfigured to turn on the bleeder so that the bleeder generates thesecond current, and the control signal at the second logic level isconfigured to turn off the bleeder so that the bleeder does not generatethe second current. As an example, the rectifying bridge is coupled tothe TRIAC dimmer through a fuse.

According to certain embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes are configured to receivea rectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator, receive an input voltagegenerated by a voltage divider, and output a control signal to thebleeder. The sensing voltage indicates a magnitude of the first current,the voltage divider is configured to receive a dimmer output voltagegenerated by the TRIAC dimmer and received by the rectifying bridge, andthe input voltage indicating a magnitude of the dimmer output voltage.The controller is further configured to generate the control signal toturn off the bleeder if the sensing voltage and the input voltagesatisfy a first condition so that the bleeder does not generate a secondcurrent, and generate the control signal to turn on the bleeder if thesensing signal and the input voltage satisfy a second condition so thatthe bleeder generates the second current. The second current is largerthan zero in magnitude. The second condition is different from the firstcondition. For example, the system is implemented according to at leastFIG. 10 .

As an example, the controller is further configured to: generate thecontrol signal at a first logic level from a first time to a secondtime, during which the sensing voltage is smaller than a first referencevoltage in magnitude and the input voltage is smaller than a secondreference voltage in magnitude; generate the control signal at a secondlogic level from the second time to a third time, during which thesensing voltage is larger than the first reference voltage in magnitudeand the input voltage is larger than the second reference voltage inmagnitude; generate the control signal at the second logic level fromthe third time to a fourth time, during which the sensing voltage issmaller than the first reference voltage in magnitude and the inputvoltage is larger than the second reference voltage in magnitude; andgenerate the control signal at the first logic level from the fourthtime to a fifth time, during which the sensing voltage is smaller thanthe first reference voltage in magnitude and the input voltage issmaller than the second reference voltage in magnitude; wherein thefirst logic level and the second logic level are different. For example,the control signal at the first logic level is configured to turn on thebleeder so that the bleeder generates the second current, and thecontrol signal at the second logic level is configured to turn off thebleeder so that the bleeder does not generate the second current. As anexample, the rectifying bridge is coupled to the TRIAC dimmer through afuse.

According to some embodiments, a system for controlling one or morelight emitting diodes includes a current generator configured togenerate a first current flowing through one or more light emittingdiodes. The one or more light emitting diodes are configured to receivea rectified voltage generated by a rectifying bridge coupled to a TRIACdimmer. Additionally, the system includes a bleeder configured toreceive the rectified voltage, and a controller configured to receive asensing voltage from the current generator, receive an input voltagegenerated by a voltage divider, and output a control signal to thebleeder. The sensing voltage indicates a magnitude of the first current,the voltage divider is configured to receive a dimmer output voltagegenerated by the TRIAC dimmer and received by the rectifying bridge, andthe input voltage indicates a magnitude of the dimmer output voltage.The controller is further configured to generate the control signal toturn off the bleeder if the input voltage satisfies a first condition sothat the bleeder does not generate a second current, and generate thecontrol signal to turn on the bleeder if the input voltage satisfies asecond condition so that the bleeder generates the second current. Thesecond current is larger than zero in magnitude. The second condition isdifferent from the first condition. For example, the system isimplemented according to at least FIG. 10 .

As an example, the controller is further configured to: generate thecontrol signal at a first logic level from a first time to a secondtime, during which the input voltage is smaller than a reference voltagein magnitude; generate the control signal at a second logic level fromthe second time to a third time, during which the input voltage islarger than the reference voltage in magnitude; and generate the controlsignal at the first logic level from the third time to a fourth time,during which the input voltage is smaller than the second referencevoltage in magnitude; wherein the first logic level and the second logiclevel are different. For example, the control signal at the first logiclevel is configured to turn on the bleeder so that the bleeder generatesthe second current, and the control signal at the second logic level isconfigured to turn off the bleeder so that the bleeder does not generatethe second current. As an example, the rectifying bridge is coupled tothe TRIAC dimmer through a fuse.

According to certain embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving the rectified voltage, receiving a sensingvoltage, the sensing voltage indicating a magnitude of the firstcurrent, and outputting a control signal to a bleeder. The outputting acontrol signal to a bleeder includes generating the control signal toturn off the bleeder if the sensing voltage satisfies a first conditionso that the bleeder does not generate a second current, and generatingthe control signal to turn on the bleeder if the sensing signalsatisfies a second condition so that the bleeder generates the secondcurrent. The second current is larger than zero in magnitude. The secondcondition is different from the first condition. For example, the methodis implemented according to at least FIG. 2 , FIG. 3 , FIG. 4 , FIG. 5 ,and/or FIG. 6 .

According to some embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving a sensing voltage, the sensing voltageindicating a magnitude of the first current, receiving an input voltage,the input voltage indicating a magnitude of the rectified voltage, andoutputting a control signal to the bleeder. The outputting a controlsignal to the bleeder includes generating the control signal to turn offthe bleeder if the sensing voltage and the input voltage satisfy a firstcondition so that the bleeder does not generate a second current, andgenerating the control signal to turn on the bleeder if the sensingsignal and the input voltage satisfy a second condition so that thebleeder generates the second current. The second current is larger thanzero in magnitude. The second condition is different from the firstcondition. For example, the method is implemented according to at leastFIG. 7 , FIG. 8 , and/or FIG. 9 .

According to certain embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving a sensing voltage, the sensing voltageindicating a magnitude of the first current, receiving an input voltage,the input voltage indicating a magnitude of the rectified voltage, andoutputting a control signal to the bleeder. The outputting a controlsignal to the bleeder includes generating the control signal to turn offthe bleeder if the input voltage satisfies a first condition so that thebleeder does not generate a second current, and generating the controlsignal to turn on the bleeder if the input voltage satisfies a secondcondition so that the bleeder generates the second current. The secondcurrent is larger than zero in magnitude. The second condition isdifferent from the first condition. For example, the method isimplemented according to at least FIG. 7 , FIG. 8 , and/or FIG. 9 .

According to some embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving a sensing voltage, the sensing voltageindicating a magnitude of the first current, receiving an input voltage,the input voltage indicating a magnitude of a dimmer output voltagegenerated by the TRIAC dimmer and received by the rectifying bridge, andoutputting a control signal to the bleeder. The outputting a controlsignal to the bleeder includes generating the control signal to turn offthe bleeder if the sensing voltage and the input voltage satisfy a firstcondition so that the bleeder does not generate a second current, andgenerating the control signal to turn on the bleeder if the sensingsignal and the input voltage satisfy a second condition so that thebleeder generates the second current. The second current is larger thanzero in magnitude. The second condition is different from the firstcondition. For example, the method is implemented according to at leastFIG. 10 .

According to certain embodiments, a method for controlling one or morelight emitting diodes includes generating a first current flowingthrough one or more light emitting diodes. The one or more lightemitting diodes are configured to receive a rectified voltage generatedby a rectifying bridge coupled to a TRIAC dimmer. Additionally, themethod includes receiving a sensing voltage; receiving an input voltage,and outputting a control signal to the bleeder. The sensing voltageindicates a magnitude of the first current, and the input voltageindicates a magnitude of a dimmer output voltage generated by the TRIACdimmer and received by the rectifying bridge. The outputting a controlsignal to the bleeder includes generating the control signal to turn offthe bleeder if the input voltage satisfies a first condition so that thebleeder does not generate a second current, and generating the controlsignal to turn on the bleeder if the input voltage satisfies a secondcondition so that the bleeder generates the second current. The secondcurrent is larger than zero in magnitude. The second condition isdifferent from the first condition. For example, the method isimplemented according to at least FIG. 10 .

According to certain embodiments, the present invention can beimplemented in other examples without departing from one or moreessential characteristics. As an example, various embodiments are to beconsidered in all aspects as exemplary but not limiting.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. As an example, some orall components of various embodiments of the present invention each are,individually and/or in combination with at least another component,implemented in one or more circuits, such as one or more analog circuitsand/or one or more digital circuits. For example, various embodimentsand/or examples of the present invention can be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system for controlling one or more lightemitting diodes, the system comprising: a current generator configuredto generate a first current flowing through one or more light emittingdiodes, the one or more light emitting diodes being configured toreceive a rectified voltage generated by a rectifying bridge coupled toa TRIAC dimmer; a bleeder configured to receive the rectified voltage;and a controller configured to receive a sensing voltage from thecurrent generator and output a control signal to the bleeder, thesensing voltage indicating a magnitude of the first current; wherein:the controller includes a comparator configured to receive the sensingvoltage and the reference voltage and generate a comparison signal basedon the sensing voltage and the reference voltage; the controller furtherincludes a delay circuit; the delay circuit includes a single inputterminal; the single input terminal of the delay circuit is directlycoupled to the comparison signal; the delay circuit is configured togenerate the control signal based on the comparison signal; and thedelay circuit is further configured to output the control signal.
 2. Thesystem of claim 1 wherein the controller is further configured to:generate the control signal to turn off the bleeder if the sensingvoltage satisfies a first condition so that the bleeder does notgenerate a second current, the second current being larger than zero inmagnitude; and generate the control signal to turn on the bleeder if thesensing signal satisfies a second condition so that the bleedergenerates the second current; wherein: the first condition is thesensing voltage being larger than a reference voltage in magnitude; andthe second condition is the sensing voltage being smaller than thereference voltage in magnitude.
 3. The system of claim 1 wherein: thecontroller includes a comparator configured to receive the sensingvoltage and a reference voltage; and the controller is furtherconfigured to change the control signal to turn off the bleeder inresponse to the sensing voltage becoming larger than the referencevoltage in magnitude.
 4. The system of claim 3 wherein the controller isfurther configured to change the control signal to turn on the bleederin response to the sensing voltage becoming smaller than the referencevoltage in magnitude.
 5. The system of claim 4 wherein the controller isfurther configured to change the control signal to turn on the bleeder,without a delay, in response to the sensing voltage becoming smallerthan the reference voltage in magnitude.
 6. The system of claim 1wherein the controller is further configured to: generate the controlsignal at a first logic level from a first time to a second time, duringwhich the sensing voltage is smaller than a reference voltage inmagnitude; generate the control signal at a second logic level from thesecond time to a third time, during which the sensing voltage is largerthan the reference voltage in magnitude; and generate the control signalat the first logic level from the third time to a fourth time, duringwhich the sensing voltage is smaller than the reference voltage inmagnitude; wherein the first logic level and the second logic level aredifferent.
 7. The system of claim 6 wherein: the control signal at thefirst logic level is configured to turn on the bleeder so that thebleeder generates the second current; and the control signal at thesecond logic level is configured to turn off the bleeder so that thebleeder does not generate the second current.
 8. The system of claim 1wherein: the controller includes a comparator configured to receive thesensing voltage and a reference voltage and generate a comparison signalbased at least in part on the sensing voltage and the reference voltage;and a control signal generator configured to receive the comparison andgenerate the control signal based at least in part on the comparisonsignal.
 9. The system of claim 8 wherein the control signal generator isfurther configured to change the control signal to turn on the bleeder,with a predetermined delay, in response to the sensing voltage becomingsmaller than the reference voltage in magnitude.
 10. The system of claim9 wherein the controller is further configured to: generate the controlsignal at a first logic level from a first time to a second time, duringwhich the sensing voltage is smaller than the reference voltage inmagnitude; generate the control signal at a second logic level from thesecond time to a third time, during which the sensing voltage is largerthan the reference voltage in magnitude; generate the control signal atthe second logic level from the third time to a fourth time, duringwhich the sensing voltage is smaller than the reference voltage inmagnitude; and generate the control signal at the first logic level fromthe fourth time to a fifth time, during which the sensing voltage issmaller than the reference voltage in magnitude; wherein: the firstlogic level and the second logic level are different; and a timeduration from the third time to the fourth time is equal to thepredetermined delay in magnitude.
 11. The system of claim 1 wherein therectifying bridge is coupled to the TRIAC dimmer through a fuse.
 12. Asystem for controlling one or more light emitting diodes, the systemcomprising: a current generator configured to generate a first currentflowing through one or more light emitting diodes, the one or more lightemitting diodes being configured to receive a rectified voltagegenerated by a rectifying bridge coupled to a TRIAC dimmer; a bleederconfigured to receive the rectified voltage; and a controller configuredto: receive a sensing voltage from the current generator, the sensingvoltage indicating a magnitude of the first current; receive an inputvoltage generated by a voltage divider, the voltage divider beingconfigured to receive the rectified voltage, the input voltageindicating a magnitude of the rectified voltage; and output a controlsignal to the bleeder; wherein the controller is further configured to:generate the control signal at a first logic level from a first time toa second time, during which the sensing voltage is smaller than a firstreference voltage in magnitude and the input voltage is smaller than asecond reference voltage in magnitude; generate the control signal at asecond logic level from the second time to a third time, during whichthe sensing voltage is larger than the first reference voltage inmagnitude and the input voltage is larger than the second referencevoltage in magnitude; and generate the control signal at the secondlogic level from the third time to a fourth time, during which thesensing voltage is smaller than the first reference voltage in magnitudeand the input voltage is larger than the second reference voltage inmagnitude; wherein the first logic level and the second logic level aredifferent.
 13. The system of claim 12 wherein the voltage dividerincludes a plurality of resistors connected in series and biased betweenthe rectified voltage and a ground voltage.
 14. The system of claim 12wherein the controller is further configured to: generate the controlsignal at the first logic level from the fourth time to a fifth time,during which the sensing voltage is smaller than the first referencevoltage in magnitude and the input voltage is smaller than the secondreference voltage in magnitude.
 15. The system of claim 12 wherein thecontroller is further configured to: the control signal at the firstlogic level is configured to turn on the bleeder so that the bleedergenerates the second current; and the control signal at the second logiclevel is configured to turn off the bleeder so that the bleeder does notgenerate the second current.
 16. The system of claim 12 wherein therectifying bridge is coupled to the TRIAC dimmer through a fuse.
 17. Amethod for controlling one or more light emitting diodes, the methodcomprising: generating a first current flowing through one or more lightemitting diodes, the one or more light emitting diodes being configuredto receive a rectified voltage generated by a rectifying bridge coupledto a TRIAC dimmer; receiving the rectified voltage; receiving a sensingvoltage, the sensing voltage indicating a magnitude of the firstcurrent; and outputting a control signal to a bleeder; wherein theoutputting the control signal to the bleeder further includes:generating a comparison signal based on the sensing voltage and thereference voltage; generating, by a delay circuit, the control signalbased on the comparison signal, the delay circuit including a singleinput terminal, the single input terminal of the delay circuit directlycoupled to the comparison signal; and outputting, by the delay circuit,the control signal.
 18. A method for controlling one or more lightemitting diodes, the method comprising: generating a first currentflowing through one or more light emitting diodes, the one or more lightemitting diodes being configured to receive a rectified voltagegenerated by a rectifying bridge coupled to a TRIAC dimmer; receiving asensing voltage, the sensing voltage indicating a magnitude of the firstcurrent; receiving an input voltage, the input voltage indicating amagnitude of the rectified voltage; and outputting a control signal tothe bleeder; wherein the outputting the control signal to the bleederfurther includes: generating the control signal at a first logic levelfrom a first time to a second time, during which the sensing voltage issmaller than a first reference voltage in magnitude and the inputvoltage is smaller than a second reference voltage in magnitude;generating the control signal at a second logic level from the secondtime to a third time, during which the sensing voltage is larger thanthe first reference voltage in magnitude and the input voltage is largerthan the second reference voltage in magnitude; and generating thecontrol signal at the second logic level from the third time to a fourthtime, during which the sensing voltage is smaller than the firstreference voltage in magnitude and the input voltage is larger than thesecond reference voltage in magnitude; wherein the first logic level andthe second logic level are different.